This changes the allocation API, in the following way:
js_malloc -> {cx->,rt->,OffTheBooks::}malloc
js_calloc -> {cx->,rt->,OffTheBooks::}calloc
js_realloc -> {cx->,rt->,OffTheBooks::}realloc
js_free -> {cx->,rt->,Foreground::,UnwantedForeground::}free
js_new -> {cx->,rt->,OffTheBooks::}new_
js_new_array -> {cx->,rt->,OffTheBooks::}new_array
js_delete -> {cx->,rt->,Foreground::,UnwantedForeground::}delete_
This is to move as many allocations as possible through a JSContext (so that they may be aken into account by gcMallocBytes) and to move as many deallocations to the background as possible (except on error paths).
